1. Field of the Invention
The present invention relates to a gas pressure testing device used to check whether the pressure of gas encapsulated in a gas compartment portion of a bag is within a preset range or not.
2. Description of the Related Art
Japanese Patent No. 4,771,785 describes a rotary packaging apparatus that includes a gas charging apparatus. This rotary packaging apparatus is provided with multiple pairs of left and right bag-conveying grippers that intermittently convey bags, which are equipped with gas compartment portions, along a circular bag conveying path. Each pair of the grippers clamps or securely holds in between each one of the bags equipped with gas compartment portions at the top portion of the two lateral edges and conveyed the bag along the predetermined bag conveying path. While being conveyed, the bag is filled with a material to be packaged, and also gas is injected into its gas compartment portion. The mouth of the bag is subsequently sealed to enclose the packaged material inside the bag in an air-tight manner and simultaneously encapsulate gas in the gas compartment portion using the gas charging apparatus. A part of gas charging apparatus is disclosed in Japanese Patent No. 5,104,073 as well.
The gas compartment portion of a bag is formed in an integral manner in the lengthwise or longitudinal (height) direction of the bag between the sheets of film constituting the front and rear portions of an edge seal portion (fused portion) of the bag. The gas compartment portion is formed in such a seal portion so that the front and rear film sheets are not sealed (fused) together.
The gas compartment portion imparts shape retention properties and a self-supporting properties to the bag. Charging compressed air into the gas compartment portion can impart shape retention properties and a self-supporting capabilities to the bag. In addition, a gas compartment portion charged with compressed gas can be used, for example, as a handle for holding the bag during removal of packaged material from the bag.
Although not disclosed in Japanese Patent Nos. 4,771,785 and 5,104,073, the pressure of the gas charged in a gas compartment portion must be maintained within a predetermined range. In other words, when the pressure of the gas in a gas compartment portion is too low, it is impossible to accomplish the original purpose of the gas compartment portion that is to imparting the bag with shape retention properties and a self-supporting capabilities. Further, when the pressure of the gas charged is too low, then the gas compartment portion cannot be used as a handle. On the other hand, when the pressure of the gas charged in a gas compartment portion is too high, the pressure causes the sealed portion around the gas compartment portion (non-sealed portion) to delaminate, thereby degrading the appearance of the bag as a packaged product.
In order to keep the pressure of the gas charged into the gas compartment portion within a predetermined range, it is necessary to conduct numerous experiments in advance and precisely adjust various injection conditions, such as the pressure of the gas discharged from the nozzle of the gas charging apparatus, the spring rate of the compression spring (see the compression spring 18 of Japanese Patent No. 4,771,785), and the gap between the nozzle and the receiving member (see FIG. 5 of Japanese Patent No. 5,104,073). However, in actual operation, there are cases that some packaged products (defective articles) are produced, in which the pressure of the gas in the gas compartment portion deviates from the predetermined range.
On the other hand, it is believed that if the pressure of the gas in the gas compartment portion can be immediately tested for individual bags in an inline manner (on the same bag conveying path as the one used during the gas filling step and gas charging step), then such defective articles can be easily eliminated whenever they are produced; and, in addition, the generation of defective articles can be minimized by adjusting the conditions of the gas injection pressure as needed. However, such testing equipment is not available presently.